1. Field of the Invention
The invention relates to an apparatus and a met hod for analyzing the amount of chemical substrates in a liquid, more particularly a clarified solution.
2. Description of Prior Art
In conventional process engineering systems, such as for clarifying waste water by process water treatment plant, for example, it is necessary to check the results of treatment. Treatment quality mainly depends on how high the residual concentration of phosphates, nitrates and ammonium/nitrogen compounds is, remaining in solution. For this purpose use is made of a method of analysis in which the process water is fed to an apparatus comprising a filter unit and an analyzer. Firstly, the process water is passed through the filter unit, more particularly a membrane filter. This membrane filter has the task of holding back solid particles in the process water so that the process water is supplied to the analyzer in a suitable form to enable the concentration of phosphates, nitrates and ammonium/nitrogen compounds to be analyzed. The analyzer is a highly-sensitive measuring instrument connected to further electronic components, this being the reason why it is usually located in a laboratory. Conventionally, the filter medium is located in the process water treatment tank and is connected to the analyzer via a pipe through which the liquid to be analyzed flows. One disadvantage of this existing process configuration is that this pipe is usually very long due to the laboratory being a long way away from the process water treatment tank. When the liquid required for analysis is piped over long distances the concentration of substrates to be analyzed, more particularly phosphates, nitrates and ammonium/nitrogen compounds may change since chemical reactions also take place in this feeder pipe which tend to alter the concentration. Another disadvantage of this existing process configuration is that said feed pipe to the analyzer is usually located outside of a building and thus a heating means needs to be provided, especially in winter, so that the liquid to be analyzed cannot freeze up. The susceptibility of the feed pipe freezing up is also so high because the throughflow capacity of the membrane filter is restricted and only a small amount of the liquid to be analyzed is delivered by the membrane filter. This is why it is necessary to make use of a small pipe diameter which is then, however, even more susceptible to freezing up.
It is thus the object of the invention to eliminate the disadvantages as described above and to provide a method and an apparatus permitting precise analysis of the amount of chemical substrates in a liquid with no problem.
The gist of the invention is to provide an apparatus having a separate self-contained filtration space making it possible to implement sample treatment separate from the clarifying tank and in the vicinity of the analyzer. As a result of this arrangement said feed pipe for the filtrate to the analyzer can now be maintained as short as possible. The filtration device thus comprises a separate filtration housing to which the process water is fed, and a gas supply means arranged in the filtration housing provided for charging or flushing the filter medium immersed in the liquid with a flow of gas which prevents, or at least delays, the filter medium from clogging up with dirt particles. The process water feed to the filtration housing is made with a volume flow whichxe2x80x94as compared to that of the filtration feedxe2x80x94is very high and by means of a pipe dimensioned correspondingly stronger, as a result of which freezing up in winter operation may be effectively avoided. In this arrangement the filtration device is embedded in a circuit in which excess process water is returned back to the process water treatment tank, more particularly to the clarifying tank.
Feeding the filtrate from the filtration device to the analyzer is done either via a very short feed pipe due to the close vicinity of the filtration housing to the analyzer and/or in a temperature-controlled environment, e.g. in an operations building. Accordingly, feeding the filtrate is undisturbed and independent of seasonal changes. The combined effect of the features as described above is an enhanced measuring accuracy. When advantageously making use of a short filtrate feed pipe to the analyzer, chemical reactions in the feed pipe capable of falsifying the chemical substrate concentrations of actual clarifying are avoided.
It is possible in principle to direct a gas flow into the filter medium, In one advantageous aspect the filter medium, more particularly a sheet membrane filter, is arranged above said gas supply means, however, so that the gas bubbles rising to the surface of the membrane produce turbulences resulting in a balance between influent due to filtration and effluent due to turbulences materializing, it being this effluent as just described that is used to control a process which maintains the membranes continually functionable or at least delays clogging up of the filter medium.
For feeding both of the process water into the filtration housing and the filtrate to be analyzed into the analyzer a separate pump may be provided. To save investment costs it is possible to integrate the gas supply means in the frame to which the membrane filter is secured. This is achieved by configuring the lower part of the frame as a gas feeder and providing it with orifices permitting discharge of the gas into the process water in the filtration housing of the filtration means. This gas may be to advantage air since the gas is subject to no further requirements than to create said turbulences at the surface of the membrane. To advantage a blower may be used which introduces the gas into the filtration housing of the filtration means.
In another advantageous aspect of the invention several filter media may be arranged in a single filtration housing to thus increase the effective filter surface and thus the desired filtrate quantity. However, the filter media may also be operated alternatingly to then achieve a more effective cleaning capacity due to the effect of the turbulences of the gas flow on the membrane not operated for arresting the substrate. In addition this also creates the possibility of backwashing the membranes as well as the discharge pipes of these membranes not involved in the filtration function without having to interrupt actual filtration operation.
Advantageously a controller is provided for controlling alternating operation of the filter media between filtration and backwashing.
Should it be necessary to remove the filtration device for mainteance or repair a bypass incorporating a shutoff device is provided connecting the process water feed pipe, so that the liquid may be returned with no problem in bypassing the filtration device. A drain integrated in the system ensures that excess process water together with the arrested solid particles is returned to the clarifying tank. It is thus further assured that the filtration device always receives or discharges a fresh supply of process water and that the liquid to be analyzed has not aged by the time it attains the analyzer.
To ensure simple and reliable control of the complete apparatus a control center may be provided which enables each and every step in the process such as supplying the gas, supplying the process water, piping the liquid to be analyzed, including alternating operation by the aforementioned control unit, to be implemented. This may also be achieved by a controller for the analyzer.
For the method as described to function, making use of sheet membrane filters is not a mandatory requirement, i.e. conventional membrane capillaries or filter media shaped otherwise may also be employed.